A huge company might have a support email address of firstname.lastname@example.org. Emails that are sent to this email address are not received by a single person and then forwarded to an account manager, they typically go into a customer management system. Their subject, reply identifier and who it is from are matched with on going emails hidden behind support tickets and the whole thing is tied together in a way that allows customer service executives to analyse how well they are dealing with their customers.
These systems cost a lot of money, require people to run and generally don't make sense to have unless you have more than one person doing the same job role. If you have a small company where there is one salesman, one accountant, a couple of techies and a managing director then a standard issue tracking system will suffice. In this kind of company everybody knows their customers and can enter information into a tracker, and if Bob isn't in today then he'll get to them tomorrow because he is the only person who knows how to handle that particular enquiry.
But what happens when Bob leaves, goes on paternity leave or has a serious accident. When you work for a company with the customer management system this is not an issue because those emails were never sent to Bob, they were sent to a pool of people logged into a management system. All Bob's business relations have been sending their enquiries to email@example.com so how do we tell Bob's contacts that they must start using a different email address. Here in lies the problem.
What most small companies do is they change Bob's password and various other people log into his email account and essentially pretend to be him. This is open to all kinds of problems. Bob might use his work email for his personal banking for example. You as a company are opening Bob up for an unscrupulous employee to steal his identity. There is always the question of who owns the email account and the email in it. The users think they own it when in fact the company owns it. This can also be a bone of contention when Bob returns from his operation only to find out that is colleagues have been through his personal mail while he was away and know about the nature of his sensitive operation or his ongoing affair with the secretary.
Another side effect of trying to reuse Bob's account after he leaves is that there is no handover. Bob's account is left open and if you pay per email address (like with Google) then this is costing you money. The excuse of we need Bob's email history is a poor one as services exist to transfer email from one account to another. [ Small plug for me, use my contact form to ask about our email transfer services. ] Generally what happens is that the company is now paying for a lot of email addresses from people that have left because they are too frightened of missing something instead of creating a procedure to handle a person leaving.
What I generally advise my customers to do is think about the roles that your company does that lead you to interact with the outside world. For example your internet account, web hosting account and domain names, all your social media accounts might be the responsibility of Bob. While your HMRC VAT account, accountant, auditor, companies house might be the the responsibility of Sarah. You may have to hire seasonal staff to do maintenance services in summer because more people come through the gate as a result there is more damage or vandalism. It might not be the same person each year but they would still need to be registered with trade suppliers and the like. In the winter there is not enough work for a whole extra person and Bob would handle it.
If Sarah or Bob leave it can be a real nightmare changing all those email addresses you have registered with Twitter or the Revenue. Forms usually have to be filled in, signatures and declarations have to be made by post, the whole process can take a long time and is subject to all kinds of delays. To use our example if Bob signs up for a new internet social media network or a new cloud sharing system site he will use the email alias assigned for that role e.g. "firstname.lastname@example.org", but if he signs up for a tools manufacturer's monthly newsletter he'll use "email@example.com". If Sarah has to sign up for corporation tax online she might use the email address "firstname.lastname@example.org". Your companies internal IT person would create an alias for "it" and "accounts" and make them point to Bob and Sarah respectively. The alias "maintenance" would be assigned to Bob in the winter and then re-assigned to whom ever they hired during the summer months.
Now it is simple for the company to continue its services with external organisations when Bob is replaced with Jeff. The internal IT person will simply redirect email@example.com to firstname.lastname@example.org. The external companies don't need to know or care that you have made a staff change.
The granularity of this is worth spending time thinking about though. Sure you can have one email for every service you sign up for but there is an administrative overhead for all of this. Part of that overhead lies with your IT department but mostly it becomes about managing all those accounts on different systems and their related different passwords. Generally speaking think in terms of roles and responsibilities and you won't go far wrong.